Some windows utilize frames made from metal, e.g., aluminum alloy. Metal windows are in use in residential and commercial buildings, e.g., in storefronts and in curtain walls used on the façade of high-rise buildings. The energy transfer characteristics of windows are an important factor in the overall energy efficiency of a building and there is a continued demand for building features and methods of construction that improve energy efficiency. Aesthetic considerations also play an important part in architectural design, including the design of window systems and curtain walls. Improved and/or alternative structures and methods for controlling the heat transfer characteristics of windows, window structures, curtain walls and curtain wall assemblies and for achieving aesthetic design objectives remain desirable.